A 75-year-old man who complained of progressive dyspnea was admitted to our hospital. He had been treated with rebamipide at an outpatient clinic for the preceding seven months. Atrial blood gas values obtained on admission indicated hypoxemia. Chest radiographs and CT films revealed diffuse interstitial infiltration and minimal pleural effusion. Bronchoalveolar lavage fluid showed an increase in the total cell number, the percentages of eosinophils and lymphocytes, and a decrease in the CD4/CD8 ratio. Transbronchial lung biopsy specimens had thickened alveolar septa with lymphocyte infiltration within the air spaces. After the discontinuation of rebamipide, oral prednisolone was administered, and the patient's symptoms and pulmonary shadows quickly improved. A lymphocyte stimulating test for rebamipide was positive. A challenge test for rebamipide was not performed because informed consent could not be obtained. On the basis of these findings, our diagnosis was rebamipide-induced pneumonitis.